Honda RC250M 2001

Finishing the Honda CR60R engine and putting it in an engine stand on my workbench lead me to the idea that my new workshop needed an engine-stand-workbench-beauty. I always played with the idea of building a 250cc two stroke engine, and which type I should use for that build. Then I stumbled across a complete HRC right side engine cover on ebay to fit a 92-01 Honda CR250R engine and bought it right away.

I began collecting more and more HRC parts for the engine until I had all the parts needed to start building, but then I found some 2000/2001 chassis parts… I couldn’t help buying them and so a new search began: I am going to build a complete 2001 works Honda RC250M! Various editions of 2001 RC250M’s have been around but the one I am going to build is Yoshitaka Atsuta’s All Japan Championship winning 2001 RC250M. I like the looks of this bike and actually found a lot of parts that were specifically used by the Japanese HRC team.

Yoshitaka Atsuta’s 2001 Honda RC250

I will try to make this a 100% works bike, loaded with all the original HRC parts and build with the same care as the factory mechanics did back in the day (and still do so now !). Please check this page regularly as I will be posting updates regularly!

Sourcing engine parts

The engine on Yoshitaka Atsuta’s 2001 Honda RC250M is a full works engine with all the bells and whistles from HRC. Most of you will remember the cool magnesium Honda Racing covers and the beautiful exhaust pipe with kevlar silencer from back in the day. My goal is to find all the correct HRC parts for this engine.

As far as the works internals go, I’ve made a list of the parts that are needed. Stripe through means I have the part.

Every aspect of a works bike is special. A lot of care and attention to detail went into producing parts that are high performance as well as reliable. As the engines of the 2001 RC250M’s didn’t differ much from Japan to Europe to the US, the chassis did differ a lot. A lot of options were available to suit rider preference as well as different color combinations between teams. Yoshitaka’s 2001 bike looked a lot different compared to the Euro and US bikes due to it’s red color scheme.

Like for the engine internals, I’ve put together a list of parts that are needed to complete the chassis of this 2001 Honda RC250.

Frame modification #1

The first of three modifications is done, fabricating and welding the mounting tabs for the works skidplate. I have made the tabs from 3mm aluminium and carved them into the same shape as radiator mounts. The nuts used are from Nippon Japan, called the M6 ST Nut , which is pressed into the aluminium. Next frame mod is fitting mounts for the right side engine guard.

The RC crankshaft

The factory engine has a lot of HRC internals which were very hard to find. Luckily I found the most worshiped part: the RC crankshaft. These RC cranks are tunable for different power-band characteristic’s by altering the rotating inertia. Steel, tungsten, aluminium and nylon inserts were available and gave the tuner the flexibility to adjust the power-band simply by changing the weights. The process to change the weights is very simple as they are held in by snap-rings located in the crank flywheels. Even though the crank flywheels look like they are made from billet, they are actually made from several machined pieces that are hollow in strategic areas and then electro laser welded together. The conrod is machined of a special low carbon steel, hardened and then polished to a very low surface roughness. Very few of these were made and they would cost as much as a new production bike to produce.

Next step is prepping the cases, removing all casting marks and vapour blasting them for a smooth and good looking surface.

Frame modification #2

The second frame modification is making the mounts for the engine guard on the right hand side of the frame. Two holes had to be drilled where aluminium bushes with M8 thread have been welded in.

Frame modification #3

The final frame modification was a reinforcement of the steering head, only applied to the Japanese factory bikes in 2000 and 2001. Two triangular aluminium plates are used to get a more rigid connection between the main frame tube and the casted steering head.

Finishing the frame

I thought I was finished modifying the frame but I wasn’t. On a small picture from a Japanese magazine I discovered a triangular brace underneath the steering head on one of the photos. I quickly replicated it in 7000 series aluminium and had it welded to the frame on both sides. Afterwards the frame received a special surface treatment which not only cleaned the complete frame but also changed the surface structure to reduce adhesion of dirt, which this bike will probably never see…

Factory Friday

After a year of absence due to a home renovation project I have continued building the 2001 RC250M. Although I didn’t have time to start assembling the bike, I did find some nice parts to complete the bike even more!

Above is a 2002 set of factory Showa suspension, slightly different than used in 2001, but nevertheless an extremely rare find and very nice addition to the bike. The forks probably started their journey in 2002, Japan. Which rider they belonged to is unknown. The upper tubes were once replaced by the more matte anodized 2007-2008 tubes because of damage to the original kashima coated tubes. The lugs are pieces of CNC art, as is the shock body. The shock can be identified by the recessed area on the bladder where the Showa decal is, this type of shock was used in 2002-2003. I will have the preload rings and cups reanodized.

Decals

Decals are key in making a good looking replica bike. Today any decals or graphics can easily be replicated by the many, many decal shops around in the MX scene. But finding the original decals just adds that little more excitement and authenticity.

The Japanese factory bikes have that clean OEM look but still look trick. That’s the main reason I wanted to build this bike, along with the fact that not many other people do so too. As decals are the finishing touch to my bike, and the bike has a long way to go before I can apply them, I didn’t pay much attention at finding the decals. And like sourcing with most of the factory parts, stop paying attention and they will pop up out of nowhere! I got the HRC radiator shroud decals, small RST-1 filteroil airbox decals and the huge original fluorescent red Showa fork decals.

Building the engine

The moment is there… After about four years of collecting parts the original idea of building a factory 250 Honda powerplant has succeeded, well amost, I still need the ignition!

The cases were cleaned and new bearings were installed. While I try to perfectly restore most of the parts on the bikes I build I chose not to restore the cases with techniques like vapourblasting or chemical cleaning. I chose to keep them as authentic as possible like they were used by the team, only lightly cleaned with a soft abrasive pad. Once done the filling began…

The factory gearbox was completely gone through, with all new shims and bushes and works smoothly. An exciting find a few weeks back was an original magnesium clutch cover, which is rare because it was never sold publicly like the version offered in the kit early to mid 90’s. It’s a bit worn on the outside and like the cases I’ll keep this part as is.

A quick mock up of the engine, as it’s clutchless. I haven’t purchased the Hinson basket and inner hub yet. Also the complete ignition is missing, but when found these parts can easily be installed.

Magnesium Honda Racing ignition cover, you can see the corroded surface clearly on this picture.

Off course I couldn’t resist fitting the engine into the frame and I must say, I am starting to like it more and more. The seat is actually one off Ryuichiro Takahama’s factory seats he raced with in 00-01. It has a custom ribbed cover for more grip.

Starting to look like a bike

So in the past few weeks I have worked a lot on the bike, both engine and chassis. The factory crankshaft uses a modified stock primary gear. A friend with the original HRC primary gear was nice enough to give me the dimensions to have it modified on the lathe. The HRC primary gear is a little bit narrower, so it can be mounted with a circlip instead of the original bolt/washer setup.

Although some plastic parts are factory, or modified, most of it is just stock plastic. I found NOS fenders radiatorlouvres, forkguards and radiatorshrouds. The sidepanels will be modified red UFO items. I removed the stock decals from the radiator shrouds and applied the original HRC decals from the 2001 Japanese factory team. Well, let the pictures speak for themselves.

Radiators are stock items with a HRC high pressure 1.8 black radiatorcap. I am still looking for the factory reinforced Toyo Radiators.

Magnesium Showa fork tops

Billet HRC suspension linkage

Triple clamp setup. The triple clamps are CNC machined items with titanium stem to fit the massive factory Showa forks. The barclamp is the type which most Japanese riders would use and was barely used by European or US riders. At the end of the season Atsuta switched his bar setup to a Renthal Fatbar 672, I also have the 28.6mm barclamp incase I want to do the same switch. Note the safety wired drilled nuts and HRC tank vent rubber going into the stem.

Suspension update

Although being very happy with the factory suspension I already had on my bike, happiness rose when I found a period correct set of 2000/2001 forks and matching shock. Differences are minor but for me important as I intend on making this bike as genuine as possible.

The shock has a titanium nitrate copper coated shaft and the full CNC machined body has a more stock looking shape in contrast to the 2002 shock, which has the distinctive A-kit shape, where a small part of the bladder has a smaller diameter. The forks have 51mm titanium nitrate copper coated lower tubes and Kashima coated outer tubes. The internals are also made of magnesium and the axlelugs are the new, reinforced model, which HRC riders started using in the 2000 season.